Radiant energy – Invisible radiant energy responsive electric signalling – Ultraviolet light responsive means
Reexamination Certificate
1999-02-02
2002-10-29
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Ultraviolet light responsive means
C250S373000
Reexamination Certificate
active
06472669
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to flame scanners, and more specifically, to a silicon carbide photodiode based flame scanner that is suitable for use for purposes of effecting therewith individual burner flame discrimination in multi-fuel boilers and furnaces.
Flame scanners are important instruments in the operation of the combustion systems of fossil fuel-fired steam generators. To this end, flame scanners are one of the primary inputs into the burner management system with which such fossil fuel-fired steam generators are normally suitably provided. The principal function of such flame scanners is to monitor the combustion process, which is occurring within the fossil fuel-fired steam generators, and to provide a signal, based on such monitoring thereby of the combustion process within the fossil fuel-fired steam generator, when a stable flame exists so as to thereby provide therethrough an indication that it is safe to continue feeding fossil fuel into the combustion chamber of the fossil fuel-fired steam generator in which the combustion process is taking place. In the event that the flame becomes unstable, or the flame is lost completely, the flame scanner is designed to be operative to provide a loss of flame signal to the burner management system whereby the burner management system in turn is designed to be operative to shut off the fossil fuel to the fossil fuel-fired steam generator before an unsafe operating condition develops within the fossil fuel-fired steam generator.
A requirement that exists with fossil fuel-fired steam generators that employ a wall-fired firing system is that each individual burner thereof must have a flame scanner cooperatively associated therewith that is capable of establishing the presence of a flame from the burner with which the flame scanner is cooperatively associated. In contrast to fossil fuel-fired steam generators that employ a wall-fired firing system, in fossil fuel-fired steam generators that employ a tangentially-fired firing system the conventional philosophy for monitoring the combustion process, which is occurring therewith in, has been to simply establish that the so-called “fireball”, which is generated as a consequence of the combustion therewith in of the fossil fuel and air, is stable. To this end, the burner management system with which the fossil fuel-fired steam generators that employ a tangentially-fired firing system are equipped commonly utilize a two of four logic philosophy. In accordance with such two of four logic philosophy, at each elevation of the tangentially-fired firing system two of the four flame scanners on that elevation must be detecting the presence of a flame in order for it to be safe to continue feeding fuel to that elevation of the fossil fuel-fired steam generator. However, changes are today occurring in the industry whereby the operators of fossil fuel-fired steam generators that employ tangentially-fired firing systems are more and more looking to avail themselves of the same logic philosophy, insofar as flame scanning is concerned, as that which is utilized with fossil fuel-fired steam generators that employ wall-fired firing systems, that is, to provide a flame scanning means to monitor the flame of each individual burner.
Heretodate, the existing forms of flame scanners have relied on essentially two approaches to detect the presence of flame. The first of these two approaches involves the use of a photodiode to measure the light intensity from the flame. Based on such measurements an electrical current output is produced, which is proportional to the intensity of light on the photodiode. Typically, silicon and gallium phosphide photodiodes are utilized for such purpose. Moreover, frequently optical filters are employed to make the flame scanners more sensitive to particular wavelengths of light that are emitted from specific fossil fuels or under specific firing conditions. The second of these two approaches involves the use of an ultraviolet tube, which operates to produce a pulsed electrical output whose pulse rate is proportional to the intensity of the ultraviolet. In accordance with the teachings of the prior art, ultraviolet tubes historically have been the approach of choice for monitoring gas flames since the emission from the gas flame is primarily in the ultraviolet with only minimal visible light emissions. The photodiode approach, on the other hand, is used for monitoring oil flames and coal flames due to the high emissions therefrom, which are in the visible light and near infrared.
Notwithstanding the use heretofore in the prior art of the aforedescribed two approaches, it has unfortunately proven, however, to be difficult in many situations to be able to distinguish the near field burner flame from the background flame generated from adjacent burners. Generally, the primary method that is utilized for purposes of effecting a separation of the background flame from the near flame is to focus not only on an examination of the measured intensity but to also focus on an examination of the so-called “flicker frequency” of the signal from the photodiode, which is being measured. To this end, it has been found that near field flame will typically have a higher “flicker frequency” than do the background flames. Effecting a discrimination between the near field flame and the background flames has proven to be particularly difficult when the near field flame is being produced as a consequence of the firing of gas, whereas the background flames are being produced as a consequence of the firing of other forms of fossil fuels, such as oil or coal. The latter fossil fuels, i.e., oil and coal, are highly luminous, which means that the light emissions in the visible and near infrared are many orders of magnitude higher than the ultraviolet emissions being produced from the near field gas flame.
Continuing, the interference produced by the aforementioned background flames has been found to be more pronounced when silicon photodiodes are utilized. Moreover, this has been found to be so by virtue of the fact that silicon photodiodes have proven to be more responsive in the visible and near infrared spectral regions and by virtue of the fact that silicon photodiodes have been shown to not have very good response in the ultraviolet range, unless filtered. Ultraviolet tubes are sensitive in the ultraviolet range and as such may be deemed to provide better results than do silicon photodiodes under certain circumstances. However, ultraviolet tubes also have historically been shown to possess some drawbacks. Namely, ultraviolet tubes have relatively limited operational lives and mechanical shutters are typically required to provide some feedback that the tubes are operating correctly. Additionally, ultraviolet tubes require complex circuitry to permit extraction and differentiation of both intensity and flicker frequency signals.
To thus summarize, the problem with which operators of fossil fuel-fired steam generators are being faced is their need to have a flame scanner that is reliable and yet is capable of distinguishing near field flame operation over background flames. Moreover, such a flame scanner must be capable of doing so under all firing conditions and without requiring that the setpoints be changed on such a flame scanner when the type of fossil fuel being fired in the fossil fuel-fired steam generator changes.
There have been numerous modifications made over the years insofar as flame scanners that are suitable for use for purposes of effecting therewith the detection of the presence of a flame in fossil fuel-fired steam generators are concerned. By way of exemplification and not limitation in this regard, the resultant of one such modification is the flame scanner that forms the subject matter of U.S. Pat. No. 3,185,846 entitled “Ultra-Violet Radiation Flame Monitor”, which issued on May 25, 1965. In accordance with the teachings of U.S. Pat. No. 3,185,846, a device is provided for monitoring the flame in a combustion chamber, the flame being produced as a cons
Chase Paul H.
Grayson Terry M.
Kwapien Donald J.
Niziolek James M.
ABB Research Ltd.
Hannaher Constantine
Lee Shun
Rickin Michael M.
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